High-Pressure Fuel Pump and Pressure Control Device

Abstract

The present disclosure relates to a device for pressure control, including a rod and a plunger. The rod has a first end region delimiting a pressurized space and is movable along an axis between a top dead center and a bottom dead center. The plunger has a traverse substantially perpendicular to a plunger axis transmitting kinetic energy from a plunger drive to the rod in a contact region between a traverse surface and a second end region of the rod arranged opposite the first end region. The rod includes a calotte-shaped end region in the contact region of the rod and the traverse includes a calotte-shaped recess in the contact region of the traverse.

Claims

1. A high-pressure pump for pressurizing a fuel, the high-pressure pump comprising: a piston movable along a piston axis between a top dead center and a bottom dead center, a plunger with a traverse arranged substantially perpendicular to a plunger axis and transmitting kinetic energy from a plunger drive to the piston in a contact region between a traverse surface and an end region of the piston, wherein the piston includes a calotte-shaped end region in the contact region of the piston, and the traverse includes a calotte-shaped recess in the contact region of the traverse.

2. A device for influencing a pressure in a medium, the device comprising: a rod with a first end region delimiting a space filled with the medium, the rod movable along a rod axis between a top dead center and a bottom dead center; a plunger having a traverse arranged substantially perpendicular to a plunger axis for transmitting kinetic energy from a plunger drive to the rod in a contact region between a traverse surface and a second end region of the rod arranged opposite the first end region; wherein the rod includes a calotte-shaped end region in the contact region of the rod and the traverse includes a calotte-shaped recess in the contact region of the traverse.

3. The device as claimed in claim 2, wherein the traverse includes a traverse surface in regions adjoining the calotte-shaped recess, the traverse surface having planar form substantially perpendicular to the plunger axis.

4. The device as claimed in claim 2, wherein the calotte-shaped recess is formed into the traverse surface by stamping.

5. The device as claimed in claim 2, wherein the calotte-shaped recess is arranged symmetrically about an axis which bisects the traverse perpendicularly to the longitudinal axis thereof.

6. The device as claimed in claim 2, wherein the traverse is movable radially with respect to the plunger axis, wherein the traverse is in particular inserted into the plunger without radial fastenings.

7. The device as claimed in claim 2, further comprising a recess radius of the calotte-shaped recess of the traverse greater than a rod end radius of the calotte-shaped end region of the rod.

8. The device as claimed claim 2, further comprising a rod guide having a rod guide axis, wherein a rod end radius of the calotte-shaped end region of the rod is smaller than or equal to a spacing at the top dead center of the rod, between a tangent to a rod calotte surface at the rod axis and an intersection point of the plunger axis and the rod guide axis.

9. The device as claimed in claim 2, further comprising a rod guide having a rod guide axis, wherein a rod end radius of the calotte-shaped end region of the rod is greater than a spacing, which exists at the top dead center of the rod, between a tangent to a rod calotte surface at the rod axis to an intersection point of the plunger axis and the rod guide axis, wherein a recess radius of the calotte-shaped recess of the traverse is greater than a rod end radius of the calotte-shaped end region of the rod, to such an extent, in the case of identical materials being used, that the Hertzian stress is situated in the region of contact between a planar traverse surface and a calotte-shaped end region of the rod.

10. An internal combustion valve comprising: a rod with a first end region delimiting a space filled with the medium, the rod movable along a rod axis between a top dead center and a bottom dead center to open an engine valve; a plunger having a traverse arranged substantially perpendicular to a plunger axis for transmitting kinetic energy from a plunger drive to the rod in a contact region between a traverse surface and a second end region of the rod arranged opposite the first end region; wherein the rod includes a calotte-shaped end region in the contact region of the rod and the traverse includes a calotte-shaped recess in the contact region of the traverse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In the drawings:

[0041] FIG. 1 shows a detail of an internal combustion engine having a pressure-influencing device, wherein the pressure-influencing device is a high-pressure fuel pump which is fastened by way of a flange in the internal combustion engine according to teachings of the present disclosure;

[0042] FIG. 2 shows a detail of an internal combustion engine having a pressure-influencing device without flange fastening according to teachings of the present disclosure;

[0043] FIG. 3 shows the pressure-influencing device from FIG. 1 and FIG. 2, with a calotte-shaped recess in a traverse of a plunger;

[0044] FIG. 4 shows the pressure-influencing device from FIG. 3, with angle error positions;

[0045] FIG. 5 shows the pressure-influencing device from FIG. 1 and FIG. 2, wherein the traverse does not have a calotte-shaped recess;

[0046] FIG. 6 shows the pressure-influencing device from FIG. 1 and FIG. 2, with a calotte-shaped recess in the traverse;

[0047] FIG. 7 is a schematic geometrical illustration of the pressure-influencing device from FIG. 5, for illustrating the contact angles and lever arms;

[0048] FIG. 8 is a schematic geometrical illustration of the pressure-influencing device from FIG. 6, for illustrating the contact angles and lever arms that exist;

[0049] FIG. 9 is a schematic geometrical illustration of the pressure-influencing device from FIG. 6, for illustrating ideal radius relationships of the calotte-shaped recess and of a calotte-shaped end region of a rod;

[0050] FIG. 10 is a further schematic geometrical illustration of the pressure-influencing device from FIG. 6, for illustrating ideal radius relationships of the calotte-shaped recess and of the calotte-shaped end region;

[0051] FIG. 11 shows a diagram which illustrates the radial forces, which prevail in different geometrical arrangements of the pressure-influencing device, in a manner dependent on the force acting on a rod axis according to teachings of the present disclosure;

[0052] FIG. 12 shows a pressure-influencing device according to the prior art, without geometrical errors; and

[0053] FIG. 13 shows a pressure-influencing device according to the prior art, with geometrical errors.

DETAILED DESCRIPTION

[0054] Below, the expressions rod and piston are synonymous with one another. The same applies to the expressions pressure-influencing device, engine valve and high-pressure fuel pump.

[0055] FIG. 1 shows an internal combustion engine 56 to which a pressure-influencing device 28 in the form of a high-pressure fuel pump 16 is fastened by way of a flange 44. The pressure-influencing device 28 has a plunger 10 with a plunger guide 32, with a plunger skirt 34 and with a traverse 36. Furthermore, the pressure-influencing device 28 has a rod 12 in the form of a piston 20 and a rod guide 30.

[0056] FIG. 2 shows a pressure-influencing device 28 with plunger 10 and plunger guide 32 and plunger skirt 34 and with rod guide 30 and rod 12. In the case of the internal combustion engine 56 shown in FIG. 2, no flange 44 is provided.

[0057] FIG. 3 schematically illustrates the pressure-influencing device from FIG. 1 with flange 44, which forms a flange plane 58. The pressure-influencing device 28 in the form of the high-pressure fuel pump 16 has the plunger 10 with plunger guide 30, plunger skirt 34 and traverse 36, and the rod 12 with rod guide 30. The rod 12 of the traverse 36 is driven along a rod axis 26 between a first, top dead center 60 and a second, bottom dead center 62, that is to say is moved up and down. The traverse 36 is in turn driven by way of a roller 38, which is arranged underneath the traverse 36, along a plunger axis 40, which coincides with the rod axis 26 in the idealized illustration of the pressure-influencing device 28 shown in FIG. 3. The roller 38 is driven by way of a camshaft 65 of the internal combustion engine 56.

[0058] The roller 38 and the camshaft 65 thus jointly form a plunger drive 66.

[0059] In the idealized illustration in FIG. 3, not only the plunger axis 40 and the rod axis 26 but also a plunger guide axis 50, that is to say the axis of the plunger guide 32, and a rod guide axis 52, that is to say the axis of the rod guide 30, coincide.

[0060] As can also be seen in FIG. 3, the rod 12, or the piston 20, has a clearance in the rod guide 30, and the plunger 10 also has a clearance in the plunger guide 32. Furthermore, the traverse 36 is mounted movably in the plunger skirt 34, as indicated by the arrows P, and is movable radially relative to the plunger axis 40 in all directions.

[0061] In the ideal embodiment of the pressure-influencing device 28, the traverse 36 and the rod 12 make punctiform contact in a contact region 68 of a traverse surface 70 and of a second end region 42, which is situated opposite a first end region 22, of the rod 12. In the contact region 68, the traverse has a calotte-shaped recess 72, and the rod 12 has a calotte-shaped end region 74. The calotte-shaped recess 72 does not span the entire traverse surface 70, but rather the traverse 36 has, adjacent to the calotte-shaped recess 72, a traverse surface which is of planar form perpendicular to the plunger axis 40. The calotte-shaped recess 72 may be formed into the traverse surface 70 for example by stamping. The calotte-shaped recess 72 is arranged symmetrically on the traverse surface 70, such that the lowest point of the calotte-shaped recess 72 is intersected by the plunger axis 40, which runs perpendicular to a longitudinal axis 76 of the traverse 36.

[0062] FIG. 3 shows merely an idealized illustration of the pressure-influencing device 28, whereas FIG. 4 illustrates, overlaid thereon, the conditions that actually prevail. In reality, the plunger guide axis 50 and the rod guide axis 52 and/or the plunger axis 40 and the rod axis 26 do not coincide, such that transverse forces act in addition to an axial force F.sub.a acting perpendicularly on the rod 12. Said transverse forces can be minimized by way of the combination of calotte-shaped recess 72 in the traverse surface 70 and the calotte-shaped end region 74 on the second end region 42 of the rod 12.

[0063] This is shown by a comparison between a pressure-influencing device according to the prior art, as shown in FIG. 5, and the example pressure-influencing device 28 as shown in FIG. 6. Comparing the two illustrations in FIG. 5 and FIG. 6, it can be seen that, for the same inclination of the rod axis 26 about the plunger guide axis 50, a contact point K between the calotte-shaped end region 74 and traverse 36 is considerably further remote from the rod axis 26 in the case of a pressure-influencing device 28 as per FIG. 5 than in the pressure-influencing device 28 as per FIG. 6. Said relatively large spacing also yields greater contact angles .sub.1, .sub.2 and increased acting transverse forces.

[0064] FIG. 7 illustrates the situation of the pressure-influencing device 28 from FIG. 5 schematically in a geometrical arrangement. For better understanding, the clearance in the guides 30, 32 and the concentricity error at an intersection point S between rod axis 26 and plunger axis 40 have not been illustrated, because said errors are generally very small in relation to the errors illustrated.

[0065] As can be seen in FIG. 7, the traverse 36 may have an angle error both in a positive direction and in a negative direction. Furthermore, the tilting of the rod 12 away from the plunger axis 40 yields the angle error . The contact angles .sub.1, .sub.2 result from the sum of and .

[0066] This means that the angle error may, in expedient situations, hereinafter referred to as best case, compensate the angle error , depending on sign. Said angle error may however also further increase the angle error , this being referred to hereinafter as worst case.

[0067] The sum of and results in the contact points, illustrated in FIG. 7, for the worst case (contact point 78), a neutral case (contact point 80) and for the best case (contact point 82). For the case of the contact point 78, the contact angles .sub.1, .sub.2 are shown, which are relatively large. Also shown are the acting axial force F.sub.a on the rod axis 26 and the lever arms a.sub.1 and a.sub.2, which constitute the spacing of the respective contact point 78, 80, 82 from the plunger axis 40 or from the rod axis 26. The greater the contact angles .sub.1, .sub.2, and thus the greater the lever arms a.sub.1 and a.sub.2, the greater the transverse forces acting on the pressure-influencing device 28.

[0068] FIG. 8 geometrically illustrates the situation of the pressure-influencing 28 as per FIG. 6. Here, owing to the calotte-shaped recess 72 in the traverse 36, the angle error of the traverse 36 becomes irrelevant. This means that the contact angle can only be as great as the angle error . As a result, it is also the case that only the lever arm a.sub.2 exists, that is to say a spacing between contact point K and rod axis 26, the lever arm a.sub.1, is omitted.

[0069] Altogether, this yields considerably lower transverse forces acting on the pressure-influencing device 28, which leads to considerably lower loads and considerably less wear of the pressure-influencing device 28.

[0070] In some embodiments, the Hertzian stresses may be kept constant without restriction of the production tolerances. This can be realized through selection of the radius relationships of calotte-shaped recess 72 and calotte-shaped end region 74. Here, a distinction is made between two cases. The distinguishing criterion is the condition that the Hertzian stress should not be increased in relation to an arrangement of the pressure-influencing device 28 as shown in FIG. 5. This determines whether a rod end radius 84 of the calotte-shaped end region 74 of the rod 12 can be designed to be smaller than or equal to a minimum spacing a.sub.min, at the top dead center 60 of the rod 12, between a tangent T to a rod calotte surface 86 at the point of the rod axis 26 and the intersection point S of the plunger axis 40 and the rod guide axis 52.

[0071] In the first case, it is possible for the rod end radius 84 to be designed to be smaller than the spacing a.sub.min, as illustrated in FIG. 9.

[0072] Owing to Hertzian stresses becoming too large, however, it may also not be expedient to design the rod end radius 84 to be smaller than the spacing a.sub.min. Said situationsecond caseis illustrated in FIG. 10.

[0073] In all operating states, however, it is advantageous for a recess radius 88 of the calotte-shaped recess 72 of the traverse 36 to be greater than the rod end radius 84.

[0074] In some embodiments, the dimensions ensure adequate stiffness of the traverse 36. In this way, the contact point K is always situated between the axes 50, 52 and a very small variance between worst case and best case tolerances can be realized.

[0075] FIG. 9 illustrates various situations of the rod end radius 84 for the first case. The illustration shows rod ends 48 with three different rod end radii 84. Furthermore, a stroke 90 of the rods 12 is indicated. As can be seen, the contact point 82 of the rod 12 with the largest rod end radius 84 is spaced apart from the rod axis 26 to a considerable extent. The smaller the rod end radius becomes, the smaller said spacing a.sub.2 also becomes. With a reduction of said spacing a.sub.2, the contact angle and thus the transverse forces acting on the pressure-influencing devices 28 are simultaneously also reduced. As can be seen, in FIG. 9, the situation is at its best if the rod end radius 84 is smaller than a.sub.min.

[0076] Owing to the Hertzian stresses, it may however also be expedient for the rod end radius 84 to be selected to be greater than a.sub.min, This configuration also constitutes a significant improvement in relation to the situation in FIG. 5, as long as the recess radius 88 has a minimum radius which is considerably greater than the rod end radius 84.

[0077] The situationsecond caseis illustrated in FIG. 10 for two different recess radii 88. The illustration likewise shows two rods 12 with different end radii 84 in a range greater than a.sub.min. It can be seen that, in the case of the relatively small recess radius 88 for the relatively large rod end radius 84, a contact point K is realized which is spaced apart from the rod axis 26 to a considerable extent. In the case of the relatively large recess radius 88, however, the contact points K both for the relatively small rod end radius 84 and for the relatively large rod end radius 84 are situated relatively close to the rod axis 26.

[0078] FIG. 11 shows a diagram illustrating the transverse force, which acts on the pressure-influencing device 28, as a function of the axial load F.sub.a. The forces for four different arrangements of the pressure-influencing device 28 are plotted. Diagram A illustrates the force conditions for a pressure-influencing device 28 without calotte-shaped recess 72 in the traverse 36 for the best case situation, which is shown in FIG. 7 with the contact point 82.

[0079] By contrast, the Diagram C illustrates the situation for a pressure-influencing device 28 without calotte-shaped recess 72 for the worst case scenariocontact point 78 in FIG. 7.

[0080] Diagram B shows the force conditions for a pressure-influencing device 28 which has a calotte-shaped recess 72 in the traverse 36. In the diagram B, the traverse 36 exhibits radial mobility relative to the plunger axis 40.

[0081] Diagram D shows the situation of a pressure-influencing device 28 with the calotte-shaped recess 72, but in the case of the traverse 36 being fixed and not being radially movable relative to the plunger axis 40.

[0082] It can be clearly seen that the arrangement with calotte-shaped recess 72 and movable traverse 36 provides considerably better force conditions than the worst case scenario of the pressure-influencing device 28 without calotte-shaped recess 72. Since the achievement of worst case and best case cannot be controlled, and the force profile in Diagram B closely resembles the best case situation, more effectively controllable force conditions are obtained in a pressure-influencing device 28 with calotte-shaped recess 72. At the same time, the differences between Diagrams B and D show that a radially movable 36 may be very much favored.

[0083] Altogether, the calotte-shaped recess 72 generates direction-independent transverse forces which lie at a low level between best case and worst case of the pressure-influencing device 28 according to the prior art. This corresponds to a general reduction of the acting transverse forces.

[0084] Altogether, the transverse forces arising from the axial forces F.sub.a owing to geometrical discontinuities of the components can be reduced by up to 40% in relation to the worst case configuration from the prior art. The detrimental influences of the transverse forces owing to the contact angles .sub.1, .sub.2 can be largely eliminated, leading to a reduction of the transverse forces. At the same time, the perpendicularity of the traverse 36 with respect to the plunger axis 40 is virtually irrelevant, which leads to a reduction in production costs. The calotte-shaped recess 72 of the traverse 36 can be generated by way of simple stamping, which is particularly inexpensive. Altogether, the angle error is eliminated entirely, and the variance and magnitude of the overall angle error .sub.1 and .sub.2 is considerably reduced, such that, for the design process, virtually constant loads can be expected, and the best case and worst case advantageously lie close together. Additionally, with skilled pairing of the rod radius 84 and of the recess radius 88, it is even possible for .sub.1 and .sub.2 to be kept smaller than the inevitable angle error between the axes 50, 52 of the guides.

[0085] These advantages can be utilized in order to increase the axial load F.sub.a overall, to improve the service life of the guides 30, 32, that is to say increase robustness, to reduce the required guide lengths, which is associated with a reduction in costs and reduction in size of structural space, and, altogether, to increase the tolerances of the components, which likewise contributes to a reduction in costs in the production process.

[0086] In some embodiments, the calotte-shaped recess 72 may be provided in a separate slide shoe which is arranged in the plunger 10.

REFERENCE DESIGNATIONS

[0087] 10 Plunger [0088] 12 Rod [0089] 14 Piston pump [0090] 16 High-pressure fuel pump [0091] 18 Engine valve [0092] 20 Piston [0093] 22 First end region [0094] 24 Piston axis [0095] 26 Rod axis [0096] 28 Pressure-influencing device [0097] 30 Rod guide [0098] 32 Plunger guide [0099] 34 Plunger skirt [0100] 36 Traverse [0101] 38 Roller [0102] 40 Plunger axis [0103] 42 Second end region [0104] 44 Flange [0105] 46 Contact point [0106] 48 Rod end [0107] 50 Plunger guide axis [0108] 52 Rod guide axis [0109] 54 Flange surface [0110] 56 Internal combustion engine [0111] 58 Flange plane [0112] 60 First, top dead center [0113] 62 Second, bottom dead center [0114] 65 Camshaft [0115] 66 Plunger drive [0116] 68 Contact region [0117] 70 Traverse surface [0118] 72 Calotte-shaped recess [0119] 74 Calotte-shaped end region [0120] 76 Longitudinal axis of traverse [0121] 78 Contact point worst case [0122] 80 Contact point neutral case82 Contact point best case [0123] 84 Rod end radius [0124] 86 Rod calotte surface [0125] 88 Recess radius [0126] 90 Stroke [0127] Angle error (plunger guide axisrod axis) [0128] .sub.1 Contact angle (rod axisnormal to traverse at contact point) [0129] .sub.2 Contact angle (plunger guide axis/plungernormal to traverse at contact point) [0130] Angle error of traverse (angle of traverse relative to plunger guide) [0131] A Best case without calotte-shaped recess [0132] B Movable traverse with calotte-shaped recess [0133] C Worst case without calotte-shaped recess [0134] D Fixed traverse with calotte-shaped recess [0135] K Contact point between rod and traverse [0136] P Arrow [0137] S Intersection point of plunger axis/rod axis [0138] T Tangent [0139] F.sub.a Axial load/Hertzian stress/axial force [0140] a.sub.1 Spacing of contact point to plunger guide axis/plunger axis [0141] a.sub.2 Spacing of contact point to rod guide axis/rod axis [0142] a.sub.min Spacing of tangent to rod calotte surface to intersection point of plunger axis/rod axis